WASHINGTON, Aug 30 (Reuters) - The United States carried out air strikes on Saturday against Islamic State fighters near the besieged Shi'ite town of Amerli in northern Iraq and dropped humanitarian supplies to civilians in the area, the Pentagon said.

President Barack Obama authorized the operation to prevent an Islamic State attack on residents of Amerli. The aid was delivered by U.S. aircraft, along with planes from Britain, France and Australia, Pentagon spokesman Mark Wright said in a statement.

Amerli has been surrounded by Islamic State forces for more than two months. Iraqi army and Kurdish forces closed in on Islamic State fighters on Saturday in a push to break the Sunni militants' siege of the town.

Armed residents of Amerli have managed to fend off attacks by Islamic State fighters, who regard its majority Shi'ite Turkman population as apostates. More than 15,000 people remain trapped inside. (Reporting By Matt Spetalnick; Editing by Paul Tait)